Although it is known to employ a jet liquid, such as water, bearing a suspension of particulate abrasive material for cutting and cleaning purposes, this technique is not entirely satisfactory because of the limitations of the apparatus hitherto employed.
In the known apparatus, a dispenser for a jet of liquid bearing particulate abrasive material comprises a hollow body defining a bore, liquid inlet means at one end of the bore, outlet means at the other end of the bore for discharging liquid bearing particulate abrasive material, a mixing chamber disposed between the liquid inlet means and the outlet means, a supply chamber for the particulate material, and passage means for transferring the particulate material from the supply chamber to the mixing chamber. Thus when it is necessary to use a jet of liquid bearing particular abrasive material for cutting purposes, mixing of the particulate abrasive material with the pressurised liquid has been found to result in a considerable reduction in pressure of the pressurrised liquid. Further it it difficult to provide a cohesive, parallel-sided jet and, as the abrasive material is only drawn onto one side of the jet, the jet is not stable and the cut is uneven, biased to one side where the majority of the abrasive material is concentrated. Conversely, where the jet of liquid bearing particulate abrasive material is to be used for cleaning purposes, in spite of the fact that a divergent jet is advantageous in this application, there is still too much pressure loss in the pressurised liquid as a result of the mixing of the particulate abrasive material with the liquid. Moreover, in spite of this excessive pressure loss, it has been found that the particulate abrasive material is not sufficiently uniformly suspended in the liquid. As it is common practice in most cleaning heads for the liquid inlet means to comprise a plurality of water inlets arranged around a single central inlet for the abrasive material, the abrasive material forms a narrow efficient cleaning core, but this effect diminishes in the radially outer parts of the jet where the abrasive material is less concentrated.